Recently, in my area, the weather has seen a few colder days, in the 40's...my truck is seeming to react to this as when i start it up in the morning, my whole truck shakes, much like a rumble, not a knocking i dont think, and does this for about a min and a half, untill my truck heats up. Is this a normal thing or should i be concerned? Also, when my truck does heat up after driving 15 min or so, my engine temp gauge goes up to about 3/4 hot, a bit more than half temp... should i worry about this too?